- two groups: - unicellular = most protists - multicellular = animals, plants (algae & fungi) - membrane-bound organelles:

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1 Structure of Eukaryotic & Prokaryotic Cells Cells: similarities - all composed of the same sorts of molecules - all carry out the same basic chemistry - all store their genetic material as DNA - all have same basic genetic mechanisms: genetic material is replicated & passed on to next generation by cell division information flow uses the same chemical machinery - all contain the same set of 20 amino acids in their proteins same common ancestor = 3.5 billion years ago mutation & selection of descendant cells (evolution) resulted in divergence, modification, adaption, specialisation & remains ongoing Fundamental difference between prokaryotes & eukaryotes: - karyon = kernel /nucleus - pro = before - eu = truely Prokaryotes: - two groups: Eubacteria = true bacteria = found in environments similar to us Archea = found in hostile environments as well as more familiar ones division based on molecular biological characterisations they are as different from each other as either is from eukaryotes - simple cells - few micrometers long - tough, protective wall - plasma membrane - essentially no membrane-bound organelles (no nucleus = free circular DNA in cytosol) - ribosomes - may have flagellum (sperm tail thing) - can reproduce quickly e.g. some divide every 20 min - most diverse group of cells - successful inhabit many different environments - exhibit many different growth forms (spherical/rod-shaped/spiral & chains/clusters & other organised multicellular structures) - may be: organotrophic (use any organic molecule as energy source) phototrophic (use light as an energy source) lithotrophic (use sources such as nitrogen & sulphur containing compounds & iron as energy sources) Eukaryotes: - unicellular = most protists - multicellular = animals, plants (algae & fungi) - membrane-bound organelles: nucleus mitochondria chloroplasts Golgi apparatus endoplasmic reticulum endosomes, lysosomes vacuoles micro bodies e.g. peroxisomes - cytoskeleton (microtubules, action filaments & intermediate filaments) - other cell components (ribosomes & vesicles)

2 Membranes: - compartmentalise cells: separate cells from their environments separate organelles from each other & the cytosol - double membrane surrounds nucleus, mitochondria, chloroplasts - Plasma membrane involved in cell signalling, transport of solutes, cell growth & motility - bilayer of phospholipids = asymmetrical arrangement in the two halves - proteins = integral (imbedded) & peripheral (attached loosely to the bilayer) - fluid mosaic = both proteins & phospholipids can move laterally & irregular arrangement of proteins - selectively permeable: small hydrophobic & small uncharge molecules can cross freely larger uncharged polar molecules & charged solutes must interact with transmembrane proteins - carbohydrate groups: on lipid = glycolipid to proteins = glycoprotein on external (noncytosolic) side of plasma membrane play rolls in cell-to-cell communication, protection from chemical & mechanical damage & adhesion Nucleus: continuous with ER interrupted by pores = allow passage of selected molecules between cytosol & nucleus - contain most cellular DNA heterochromatin = DNA + proteins highly condensed, even at interphase euchromatin = DNA + proteins not condensed until mitosis - typically contain a nucleolus site of rrna synthesis & ribosomal subunit assembly Ribosomes: - site of protein synthesis - large complexes of proteins & rrna - eukaryotic = 80S & prokaryotic = 70S - two populations in eukaryotes cytosolic = free or attached to ER (80S) in mitochondria & chloroplasts (70S) Mitochondria: - sites of cellular respiration & major energy production (ATP from oxidative phosphorylation) - matrix: smooth outer membrane = permeable to ions & small molecules highly folded (cristae) inner membrane 1. impermeable 2. transport proteins control movement across 3. contains an electron transport chain & ATP synthase region not taken up my membranes contains DNA (codes for trna, rrna, mrna = proteins for DNA synthesis & oxidative reactions ribosomes (70S) enzymes for the tricarboxylic acid (citric acid, Krebs cycle) - mitocondria = the products of endosymbiosis ancestral eukaryotic cell ingested (not digest) an aerobic bacterium = over time evolved to mitochondrion DNA of the bacterium was either transferred to the eukaryotic host cell nucleus or lost because it was no longer required - energy production: breakdown products of digestion enter cell cytosol for gradual oxidation & production of energy (final stages in mitochondria)

3 1. glucose & other sugars converted to pyruvate through glycolysis 2. some amino acids are converted to pyruvate 3. pyruvate enters the mitochondrion 4. fatty acids enter the mitochondrion 5. pyruvate, fatty acids & some amino acids are oxidised to acetyl CoA in the mitochondrion 6. acetyl CoA is further oxidised by the citric acid cycle, producing CO 2 & reducing power in the form of NADH & FADH 2 * some amino acids can enter at intermediate steps & be oxidised directly 7. NADH & FADH 2 donate high-energy electron that move through the electron transport chain in the inner mitochondrial membrane 8. this results in the oxidation of NADH & FADH 2, the reduction of O 2 to H 2O & ATP production 9. donated electrons pass through 3 inner mitochondrial membrane complexes in a series of oxidation-reduction reactions 10. a proton gradient is generated across the inner mitochondrial membrane from the electron flow 11. mobile electron carriers (Q, c) connect electron flow through the complexes 12. ATP is synthesised as protons move through the ATP synthase from the intermembrane space into the matrix 13. ATP is transported out of the mitochondrion for use by the cell Complex I Complex III Complex IV - complex II = succinate dehydrogenase located in inner mitochondrial membrane (citric acid cycle enzyme) - where FADH 2 is produced - electrons from FADH 2 are passed to ubiquinone, then to complex III etc. Chloroplasts: - sites of photosynthesis (2 sets of reactions = light harvesting & carbohydrate production) outermsmbrane permeable to ions & small molecules - inner membrane impermeable transport proteins control movement across - internal membrane system thylakoids = light harvesting pigments & an electron transport chain & ATP synthase folded into stacks = grana & lumen = space between folded membranes (lumen)

4 - stroma region not taken up by thylakoid membranes contains DNA (codes for trna, rrna, mrna = proteins for DNA synthesis & photosynthesis) ribosomes (70S) enzymes for carbohydrate production - chloroplasts = the products of endosymbiosis: ancestral eukaryotic cell ingested = ingest, not digest, photosynthetic bacterium = evolved into a chloroplast DNA of bacterium = into host cell or lost because not required - light harvesting reactions: light energy is collected by pigments in the thylakoid membranes & converted to reducing power (NADPH) & chemical energy (ATP) through a series of oxidation-reduction reactions, with H 2O being the original electron donor & NADPH the final electron acceptor during electron transport, protons move across the thylakoid membranes from the stroma into the thylakoid lumen, generating a proton gradient ATP is synthesised as protons move back across the membrane, from thylakoid membrane into the stroma, through the ATP synthase PQ = plastoquinone Fd = ferredoxin - carbohydrate production: NADPH & ATP produced during the light reactions are used for the synthesis of carbohydrates from atmospheric CO2 int he stroma (Calvin cycle) the enzyme ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) catalyses the first reaction in the Calvin cycle & is the most abundant enzyme in the world

5 Endoplasmic reticulum: - network of sacs & tubules (cisternae) extending throughout the cytosol - synthesis of most cell membrane components & molecules exported from a cell - if ribosomes are attached = rough ER protein synthesis continuous with the nuclear membrane - if no ribosomes = smooth ER lipid synthesis Golgi Apparatus: - stacks of flattened sacs (cisternae) = one of more per cell - synthesis & packaging of molecules to be secreted from cell - routing of newly synthesised proteins to their correct cellular locations - associated with many transport vesicles - distinct orientation cis face = adjacent to ER trans face = point towards plasma membrane - transport vesicles pinch off & fuse with cisternae carry proteins being modified by the addition of sugar groups - correlation of enzyme location & what step it catalyses in sugar-modification reaction pathway Endomembrane System: - includes nuclear envelope, ER, Golgi apparatus, transport vesicles, plasma membrane, & endoscopes & lysosomes (animal cells) or vacuoles (plant cells) - outward (exocytic) pathway 1. proteins synthesised on rough ER & glycosylated 2. vesicles containing glycoproteins bud of ER & fuse with cis Golgi cisternae 3. glycoproteins are further glysocylated as they travel through Golgi cisternae by vesicle budding & fusion 4. at the trans face of the Golgi, vesicles are directed to plasma membranee or lysosome/vacuole - inward (endocytic) pathway 1. ingestion & degradation (or recycling of extracellular molecules 2. regions of the plasma membrane containing molecules to be degraded bud inward to form vesicles 3. vesicles fuse with early endoscopes 4. ultimately molecules are degraded in the lysosome/vacuole 5. some degradation products can be reused by the cell Red arrows = exocytic path Green arrows = endocytic path - vacuoles of plant cells are sites of degradation; however, they also act as storage organs (e.g. seed proteins) detoxification sites (e.g. tannins) pigment deposition (e.g. anthocyanins)